1. Field of the Invention
The present invention relates to a recording system applicable to copying machines, facsimile apparatuses, word processors, printers as an output terminal for a computer or the like, which system performs recording by discharging a recording ink through a discharge portion, a recording head used for the above-described recording system and a wiring substrate suitable for the recording head.
2. Description of the Related Art
Conventionally, full-line type ink jet recording heads having structures as illustrated, for example, in FIG. 1 have been known as a recording head.
In the head 1 illustrated in FIG. 1, an insulated substrate 3 on which there are arranged a plurality of semiconductor devices 2 such as electro-thermal converting elements and their wire bondings and an IC for driving them is placed in a row together with a flexible cable 4 on a support plate 5. The substrate 3 and the cable 4 are pressed onto the support plate 5 by a rigid holding member 6 for holding the flexible cable and five screws 7 through a rubber holder 8 so that a wiring portion of the substrate 3 and the flexible cable 4 can be fixed mechanically and connected electrically to each other. Reference numeral 9 denotes an ink feed pipe for feeding ink from both sides into a common liquid chamber 10. The ink feed pipe is composed of an elastic tube.
A part of the common liquid chamber 10 is formed by providing a member or top plate 11 composed of a resin or the like with depressions, and a part of an ink discharge portion or orifice 12 is similarly formed thereby. By bonding these on the substrate 3 a space for flowing ink therein and openings for discharging ink therethrough are formed, thus constructing the ink jet head 1.
On the other hand, FIG. 2 is a schematic perspective view illustrating a serial scanning type ink jet recording apparatus.
In FIG. 2, the head 1 having, for example, 16 to 256 discharge portions is detachably mounted on a carriage 21 which is guided on a guide shaft 20, and present invention exhibits excellent effects in this type of apparatus.
The typical structure and operational principle of this type are preferably those disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796.
On the wiring substrate 3 of the above-described conventional recording head 1 are formed an electro-thermal converting element which generates thermal energy utilized for discharging ink and a wiring portion for connecting the electro-thermal converting element to the semiconductor device 2 such as an IC for driving.
In the wiring portion is provided a bump electrode to be connected to a solder bump provided in the semiconductor device.
Referring to FIGS. 3A to 3E, an example of the structure of the bump electrode in the conventional film wiring substrate will be explained according to its production procedures.
Firstly, as shown in FIG. 3A, there are formed on the insulated substrate 3 an Al electrode 30 and also a protective layer 31 composed of an inorganic insulating layer such as a SiO.sub.2 or SiN layer or an in this state is scanned in a direction perpendicular to the direction in which recording paper 22 is conveyed. Reference numeral 23 denotes a belt conveyor for scanning the carriage 21. Reference numeral 24 denotes a conveyor roll and reference numeral 25 denotes a platen. These convey the recording paper 22 to a desired position. Further, reference numeral 26 denotes a discharge recovering apparatus for maintaining the discharge portions in good condition, which includes an elastic cap, an aspirator and the like.
The system of the above-described example is constructed such that signal outputs for driving the recording paper conveying means, head scanning means and discharge recovering means as well as those for driving the recording head can be controlled by controlling means based on instructions put out from a CPU of the main body of the ink jet recording apparatus.
Among the above-described conventional recording heads and recording systems, what is aimed at by the present invention is an apparatus of a type which discharges ink by utilizing thermal energy since the organic insulating layer such as a polyimide layer and having a circular through hole 31a.
Subsequently, as shown in FIG. 3B, on the substrate 3 are deposited by sputtering a barrier metal layer 32 made of, for example, Cr, Ti, Ni or the like and a solder connecting layer 33 made of, for example, Cu, Au, Cu-Au alloy or the like.
Over the entire surface of the substrate 3 provided with the electrode 30, the protective layer 31, the barrier metal layer 32 and the solder connecting layer 33 is coated a photoresist layer 34 by a spin coating method, a roll coating method, a dipping method, a printing method or the like, and then exposure treatment and development treatment are performed.
Thereafter, as shown FIG. 3D, the solder connecting layer 31 and the metal layer 32 are etched using the photoresist layer 34 as a mask.
Finally, as shown in FIG. 3E, the photoresist layer 34 is peeled off to complete the procedures.
In the production of the above-described conventional film wiring substrate, it is generally the case that a roll coating method is selected in the step of photoresist coating in view of the fact that the substrate is of a polygon (usually tetragon) and has a large area and in view of of productivity.
However, in the above-described conventional film wiring substrate, as shown in FIG. 3B, a circular concavity 33a of, for example, several centimeters or more in depth exists in the solder connecting layer 33 above the through hole 31a of the protective layer 31. Thus, it tends to become more difficult at every pitch of a groove of a grooved coating roll (especially, at thread portions of the roll) to carry out coating of the photoresist layer 34, resulting in that there has been a possibility that in a subsequent etching step only the through hole portions of the metal layer (i.e., the solder connecting layer 33 and in addition the barrier metal layer 32) of the concave portion 34a where coating has been carried out incompletely could be etched out.
On the other hand, electro-thermal converting elements in conventional thin film wiring substrates are constructed as follows.
Electro-thermal converting elements have heating units which convert electric energy to thermal energy to be used for discharging ink. As shown in FIGS. 4A and 4B, in order to construct an electro-thermal converting element, at first an HfB.sub.2 film 40 serving as a heat generating resistor layer and an Al film serving as an electrode 41 are formed on the substrate plate 3, for example, by sputtering or the like, followed by patterning to form an electro-thermal converting element.
Next, an SiO.sub.2 film serving as an antioxidation film 42 and a Ta film serving as anti-cavitation film 43 for the electro-thermal converting element are formed, for example, by sputtering or the like, followed by patterning.
Thereafter, a photosensitive polyimide as an ink-resistant protective film, 4 is coated thereon and patterning is carried out.
Further, the second layer, i.e., Al conductive layer 41, is partially exposed and on this exposed portion is formed a common electrode 45 which is Cu-plated. In this case, the SiO.sub.2 layer 42 and the photosensitive polyimide layer 44 underlying the common electrode 45 function as an interlayer insulator layer.
Thereafter, a plate 11 having a concave portion for forming a common liquid chamber 10 as a passage for a recording liquid and individual liquid paths 46 is bonded, and a wiring to be connected to a driving circuit which generates driving signals for driving the electro-thermal converting element is electrically connected, thus producing a liquid spray recording head (not shown).
In FIG. 4A, the heat generating resistor layer 40, the electrode 41 and the common electrode 45 are illustrated but the protective layers 42, 43 and 44 and the plate 11 are omitted.
On one end of the electrode 41 opposite to the common electrode, i.e., segment electrode, is usually formed the above-described bump electrode through which the electrode 41 is connected to a semiconductor device. It should be noted that the same is true in the case where the semiconductor device is connected to the end on the side of the common electrode 45.
In the conventional technique as described above, the common electrode 45 is placed outside the plate 11, more specifically outside the liquid paths of the recording head and therefore the part of the electrode 41 on the side of the common electrode 45 must have a length of M.sub.2 as shown in FIGS. 4A and 4B which is considerably larger than the length M.sub.1 of the part of the electrode 41 within the plate 11 and thus a considerably long high density wiring is necessary. This makes severe disadvantages involved in production such as low yield due to short circuit, disconnection or the like. That is, repeated driving of the conventional device under application of a large amount of electric current which can generate heat enough to discharge liquid causes short circuit or disconnection, resulting in that the durability of the recording head decreases unacceptably.